With conventional cosmetic products, a user typically must choose between a product that is easily removable and a product that remains on the skin for long periods of time (i.e., an entire day). Although easily-removable products can be rapidly removed by, for example, washing with soap and water, a user may find herself repeatedly reapplying the product throughout the day, as the product may also be inadvertently removed by sweat and contact with clothing or the like. On the other hand, typical long-lasting cosmetic products are less subject to inadvertent removal, but may be difficult to wash off and may require the use of organic solvents or other harsh cosmetic removers. Accordingly, there is a continuing need in the art for cosmetic compositions that remain on the skin for extended periods of time, while being easily-removable by washing with soap and water.
Certain pH-dependent products are known in the art. For example, U.S. Pat. No. 5,993,831 to Ribier et al., incorporated herein by reference in its entirety, is directed to compositions containing nanoparticles of one or more pH-dependent polymers encapsulating an oily phase containing an active agent such as a cosmetic or pharmaceutical. The nanoparticles are said to be from 100 to 1000 nm in diameter, which allows the particles to slip between the outermost corneocytes of the stratum corneum without reaching the living epidermis.
As another example, U.S. Pat. No. 4,976,961 to Norbury et al., incorporated herein by reference in its entirety, is similarly directed to cosmetic emollient oils in microcapsules of pH-dependent polymers. Norbury's microcapsules are said to range in size from 50 to 2000 μm in diameter, and are typically crushed on the skin to release the oils contained therein. The microcapsule shell is said to include organic polymers such as phenolic aldehydes, urea-aldehyes, acrylic polymers, gelatin, and agar.
U.S. Pat. No. 7,053,034 to Shefer et al., incorporated herein by reference in its entirety, is directed to a controlled-release carrier system for targeted delivery of fragrances and active ingredients onto fabric, hair, and skin. Shefer's system is said to include solid hydrophobic nano-spheres encapsulated in a pH or salt sensitive micro-spheres. The micro-spheres are described as having an average sphere size in the range of from about 20 μm (micrometers) to about 100 μm, and the nano-spheres are said to have an average sphere size in the range of from about 0.01 μm to about 5 μm. Moreover, the micro-spheres may be made from such exemplary pH-sensitive materials as copolymers of acrylate polymers with amino substituents, acrylic acid esters, and polyacrylamides. The micro-spheres of Shefer are formed from high temperature melts emulsified into an aqueous phase.
U.S. Patent App. Pub. 2006/0127427 to Vernice et at, incorporated herein by reference in its entirety, describes a surface coated abrasive material, having a water-soluble abrasive core surrounded by a coating that is substantially insoluble in aqueous media during storage but becomes substantially water soluble upon application of substantially large quantities of water or adjustment of the pH of the aqueous medium.
The cited art fails to recognize that pH-dependent polymers can advantageously provide long-wear cosmetic films that are readily removed under mild conditions by altering the pH. Accordingly, there is a continuing need in the art for pH-dependent cosmetic compositions that remain on the skin for extended periods of time, while being easily-removable, for example, by washing with soap and water.